Tracheal intubation , usually simply referred to as intubation , is the placement of a flexible plastic tube into the trachea (windpipe) to maintain an open airway or to serve as a conduit through which to administer certain drugs. It is frequently performed in critically injured, ill or anesthetized patients to facilitate ventilation of the lungs, including mechanical ventilation, and to prevent the possibility of asphyxiation or airway obstruction. The most widely used route is orotracheal, in which an endotracheal tube is passed through the mouth and vocal apparatus into the trachea. In a nasotracheal procedure, an endotracheal tube is passed through the nose and vocal apparatus into the trachea. Other methods of intubation involve surgery and include the cricothyrotomy (used almost exclusively in emergency circumstances) and the tracheotomy, used primarily in situations where a prolonged need for airway support is anticipated.

Because it is an invasive and extremely uncomfortable medical procedure, intubation is usually performed after administration of general anesthesia and a neuromuscular-blocking drug. It can however be performed in the awake patient with local or topical anesthesia , or in an emergency without any anesthesia at all. Intubation is normally facilitated by using a conventional laryngoscope , flexible fiberoptic bronchoscope or video laryngoscope to identify the glottis, though other devices and techniques are available. After the trachea has been intubated, a balloon cuff is typically inflated near the far end of the tube to help secure it in place, to prevent leakage of respiratory gases, and to protect the tracheobronchial tree from receiving undesirable material such as stomach acid. The tube is then secured to the face or neck and connected to a T-piece, anesthesia breathing circuit, bag valve mask device, or a mechanical ventilator . Once there is no longer a need for ventilatory assistance and/or protection of the airway, the tracheal tube is removed; this is referred to as extubation of the trachea (or decannulation, in the case of a surgical airway such as a cricothyrotomy or a tracheotomy).

For centuries, tracheotomy was considered the only reliable method for intubation of the trachea. However, because only a minority of patients survived the operation, physicians undertook tracheotomy only as a last resort, on moribund patients. It was not until the late 19th century however that advances in anatomy and physiology, as well an appreciation of the germ theory of disease, had improved the outcome of this operation to the point that it could be considered an acceptable treatment option. Also at that time, advances in endoscopic instrumentation had improved to such a degree that direct laryngoscopy had become a viable means to secure the airway by the non-surgical orotracheal route. By the mid-20th century, the tracheotomy as well as endoscopy and non-surgical tracheal intubation had evolved from rarely employed procedures to becoming essential components of the practices of anesthesiology , critical care medicine , emergency medicine, gastroenterology, laryngology, pulmonology and surgery.

Tracheal intubation can be associated with minor complications such as broken teeth or lacerations of the tissues of the upper airway , or potentially fatal complications such as pulmonary aspiration of stomach contents or unrecognized intubation of the esophagus. Because of this, the potential for difficulty or complications due to the presence of unusual airway anatomy or other uncontrolled variables is carefully evaluated before undertaking tracheal intubation. Alternative strategies for securing the airway must always be readily available. The incidence of serious complications is unacceptably high when undertaken by practitioners lacking adequate training and experience.

Tracheal intubation is indicated in a variety of situations when illness or a medical procedure prevents a person from maintaining a clear airway, breathing, and oxygenating the blood. In these circumstances, oxygen supplementation using a simple face mask is inadequate.

Depressed level of consciousness

Perhaps the most common indication for tracheal intubation is for the placement of a conduit through which nitrous oxide or volatile anesthetics may be administered. General anesthetic agents , opioids, and neuromuscular-blocking drugs may diminish or even abolish the respiratory drive . Although it is not the only means to maintain a patent airway during general anesthesia, intubation of the trachea provides the most reliable means of oxygenation and ventilation

Damage to the brain (such as from a massive stroke, non-penetrating head injury, intoxication or poisoning ) may result in a depressed level of consciousness . When this becomes severe to the point of stupor or coma (defined as a score on the Glasgow Coma Scale of less than 8),

Hypoxemia

Intubation may be necessary for a patient with decreased oxygen content and oxygen saturation of the blood caused when their breathing is inadequate ( hypoventilation), suspended ( apnea), or when the lungs are unable to sufficiently transfer gasses to the blood . Such patients, who may be awake and alert, are typically critically ill with a multisystem disease or multiple severe injuries .

Airway obstruction

Actual or impending airway obstruction is a common indication for intubation of the trachea. Life-threatening airway obstruction may occur when a foreign body becomes lodged in the airway; this is especially common in infants and toddlers. Severe blunt or penetrating injury to the face or neck may be accompanied by swelling and an expanding hematoma, or injury to the larynx, trachea or bronchi . Airway obstruction is also common in people who have suffered smoke inhalation or burns within or near the airway. Sustained generalized seizure activity and angioedema are other common causes of life-threatening airway obstruction which may require tracheal intubation to secure the airway.

Manipulation of the airway

Diagnostic or therapeutic manipulation of the airway (such as bronchoscopy, laser therapy or stenting of the bronchi ) may intermittently interfere with the ability to breathe; intubation may be necessary in such situations.

Tracheal intubation is not a simple procedure and the consequences of failure are grave. Therefore the patient is carefully evaluated for potential difficulty or complications beforehand. This involves taking the medical history of the patient and performing a physical examination, the results of which can be scored against one of several classification systems. The proposed surgical procedure (e.g., surgery involving the head and neck, or bariatric surgery) may lead one to anticipate difficulties with intubation.

When taking the patient's medical history, the subject is questioned about any significant signs or symptoms, such as difficulty in speaking or difficulty in breathing . These may suggest obstructing lesions in various locations within the upper airway, larynx, or tracheobronchial tree. A history of previous surgery (e.g., previous cervical fusion ), injury, radiation therapy, or tumors involving the head, neck and upper chest can also provide clues to a potentially difficult intubation. Previous experiences with tracheal intubation, especially difficult intubation, intubation for prolonged duration (e.g., intensive care unit) or prior tracheotomy are also noted.

A detailed physical examination of the airway is important, particularly:

• the range of motion of the cervical spine : the subject should be able to tilt the head back and then forward so that the chin touches the chest.

• the range of motion of the jaw (the temporomandibular joint): three of the subject's fingers should be able to fit between the upper and lower incisors.

• the size and shape of the upper jaw and lower jaw , looking especially for problems such as maxillary hypoplasia (an underdeveloped upper jaw), micrognathia (an abnormally small jaw), or retrognathia (misalignment of the upper and lower jaw).

• the thyromental distance: three of the subject's fingers should be able to fit between the Adam's apple and the chin.

• the size and shape of the tongue and palate relative to the size of the mouth.

• the teeth, especially noting the presence of prominent maxillary incisors, any loose or damaged teeth, or crowns .

Many classification systems have been developed in an effort to predict difficulty of tracheal intubation, including the Cormack-Lehane grading system,

Laryngoscopes

The vast majority of tracheal intubations involve the use of a viewing instrument of one type or another. The widespread availability of such devices means that the technique of blind digital intubation

A laryngoscope containing fiberoptics allows the larynx to be viewed indirectly, which enables the operator to see round a bend, to visualise areas that would normally be difficult to see directly, and deal with otherwise difficult intubations. The video laryngoscope uses a digital camera sensor and allows the operator to view the larynx on a monitor. Other "noninvasive" devices which can be employed to assist in tracheal intubation are the laryngeal mask airway

Stylets

An intubating stylet is a malleable metal wire which can be inserted into the endotracheal tube to make the tube conform better to the upper airway anatomy of the specific individual, thus facilitating its insertion. Stylets are commonly employed under circumstances of difficult laryngoscopy. Just as with laryngoscope blades, there are also several types of available stylets.

The Eschmann tracheal tube introducer (often incorrectly referred to as a "gum elastic bougie") is another specialized type of stylet, which can also be used to facilitate difficult intubation.

The concept of using a stylet for replacing or exchanging orotracheal tubes was introduced by Finucane and Kupshik in 1978, using a central venous catheter.

The lighted stylet is a device that employs the principle of transillumination to facilitate blind orotracheal intubation (an intubation technique in which the laryngoscopist does not view the glottis).

Tracheal tubes

A tracheal tube is a catheter that is inserted into the trachea for the primary purpose of establishing and maintaining a patent airway. Tracheal tubes are frequently used for airway management in the settings of general anesthesia, critical care, mechanical ventilation and emergency medicine. Many different types of tracheal tubes are available, suited for different specific applications. An endotracheal tube is a specific type of tracheal tube that is nearly always inserted through the mouth (orotracheal) or nose (nasotracheal). It is a breathing conduit designed to be placed into the airway of critically injured, ill or anesthetized patients in order to perform mechanical positive pressure ventilation of the lungs and to prevent the possibility of aspiration or airway obstruction.

Tracheal tubes can be used to ensure the adequate exchange of oxygen and carbon dioxide, to deliver oxygen in higher concentrations than found in air, or to administer other gases such as helium,

Originally made from latex rubber ,

In addition to cuffed or uncuffed, preformed endotracheal tubes are also available. The oral and nasal RAE tubes (named after the inventors Ring, Adair and Elwyn) are the most widely used of the preformed tubes.

Various types of endotracheal tubes are available that have endobronchial as well as endotracheal lumens (Carlens,

The "armored" endotracheal tubes are cuffed, wire-reinforced silicone rubber tubes. They are much more flexible than polyvinyl chloride tubes, yet they are difficult to compress or kink. This can make them useful for situations in which the trachea is anticipated to remain intubated for a prolonged duration, or if the neck is to remain flexed during surgery. Most armored tubes have a Magill curve, but preformed armored RAE tubes are also available. Another type of endotracheal tube has four small openings just proximal to the inflatable cuff, which can be used for suction of the trachea or administration of intratracheal medications if necessary.

Methods to confirm tube placement

No single method for confirming tracheal tube placement has been shown to be 100% reliable. Accordingly, the use of multiple methods for confirmation of correct tube placement is now widely considered to be the standard of care .

Ideally, at least one of the methods utilized for confirming tracheal tube placement will be a measuring instrument. Waveform capnography has emerged as the gold standard for the confirmation of tube placement within the trachea. Other methods relying on instruments include the use of a colorimetric end-tidal carbon dioxide detector, a self-inflating esophageal bulb, or an esophageal detection device.

Emergencies

Tracheal intubation in the emergency setting can be difficult with the fiberoptic bronchoscope due to blood, vomit, or secretions in the airway and poor patient cooperation. Because of this, patients with massive facial injury, complete upper airway obstruction, severe hypoventilation, or profuse upper airway bleeding are poor candidates for fiberoptic intubation.

Personnel experienced in direct laryngoscopy are not always immediately available in certain settings that require emergency tracheal intubation. For this reason, specialized devices have been designed to act as bridges to a definitive airway. Such devices include the laryngeal mask airway, cuffed oropharyngeal airway and the esophageal-tracheal combitube ( Combitube).

Rapid-sequence induction and intubation

Rapid sequence induction and intubation (RSI) is a particular method of induction of general anesthesia, commonly employed in emergency operations and other situations where patients are assumed to have a "full stomach". The objective of RSI is to minimize the possibility of regurgitation and pulmonary aspiration of gastric contents during the induction of general anesthesia and subsequent tracheal intubation.

One important difference between RSI and routine tracheal intubation is that the practitioner does not manually assist the ventilation of the lungs after the onset of general anesthesia and cessation of breathing , until the trachea has been intubated and the cuff has been inflated. Another key feature of RSI is the application of manual pressure to the cricoid cartilage, often referred to as the "Sellick maneuver", prior to instrumentation of the airway and intubation of the trachea.

Since the introduction of RSI, there has been controversy regarding virtually every aspect of this technique, including:

• choice of induction drug, dose and method of administration.

• avoidance of manual ventilation before tracheal intubation.

• optimal position and whether the head-up, head-down, or horizontal supine position is the safest for induction of anesthesia in full-stomach patients.

• application of cricoid pressure (the Sellick maneuver).

Named for British anesthetist Brian Arthur Sellick (1918???1996) who first described the procedure in 1961,

The Sellick maneuver is often confused with the "BURP (Backwards Upwards Rightwards Pressure) maneuver".

Cricothyrotomy

A cricothyrotomy is an incision made through the skin and cricothyroid membrane to establish a patent airway during certain life-threatening situations, such as airway obstruction by a foreign body, angioedema, or massive facial trauma.

The quickest and easiest method to perform this technique is the needle cricothyrotomy (also referred to as a percutaneous dilational cricothyrotomy), in which a large-bore (12???14 gauge ) intravenous catheter is used to puncture the cricothyroid membrane.

Several manufacturers (Cook Medical, Portex Medical, Pyng Medical, Teleflex Medical, etc.) market prepackaged cricothyrotomy kits. These kits enable one to use either a wire-guided percutaneous dilational (Seldinger) technique, or the classic surgical technique to insert a polyvinylchloride catheter through the cricothyroid membrane. The kits may be stocked in hospital emergency departments and operating suites, as well as ambulances and other selected pre-hospital settings.

Tracheotomy

Tracheotomy consists of making an incision on the anterior aspect of the neck and opening a direct airway through an incision in the trachea. The resulting opening can serve independently as an airway or as a site for a tracheostomy tube to be inserted; this tube allows a person to breathe without the use of their nose or mouth. Both surgical

Children

There are significant differences in airway anatomy and respiratory physiology between children and adults. The smaller and younger the patient, the more significant these differences are; they must be taken into careful consideration before one undertakes tracheal intubation of any pediatric patient. These anatomical and physiological differences gradually become less significant as the human body approaches a mature age and body mass index.

For infants and young children, orotracheal intubation is easier than the nasotracheal route. Nasotracheal intubation carries a risk of dislodgement of adenoids and nasal bleeding. Despite the greater difficulty, nasotracheal intubation route is preferable to orotracheal intubation in children undergoing intensive care and requiring prolonged intubation because this route allows a more secure fixation of the tube. As with adults, there are a number of devices specially designed for assistance with difficult tracheal intubation in children.

Because the airway of a child is narrow, a small amount of glottic or tracheal swelling can produce critical obstruction. Inserting a tube that is too large relative to the diameter of the trachea can cause edema. Conversely, inserting a tube that is too small can result in inability to achieve effective positive pressure ventilation due to retrograde escape of gas through the glottis and out the mouth and nose (often referred to as a "leak" around the tube). An excessive leak can usually be corrected by inserting a larger tube or a cuffed tube.

The tip of a correctly positioned tracheal tube will be in the mid-trachea, between the collarbones on an anteroposterior chest radiograph. The correct diameter of the tube is that which results in a small leak at a pressure of about of water. The appropriate inner diameter for the endotracheal tube is estimated to be roughly the same diameter as the child's little finger. The appropriate length for the endotracheal tube can be estimated by doubling the distance from the corner of the child's mouth to the ear canal. For premature infants internal diameter is an appropriate size for the tracheal tube. For infants of normal gestational age, internal diameter is an appropriate size. For normally nourished children 1 year of age and older, one can apply the following formulas to estimate the proper diameter and depth of insertion for tracheal tubes:

• Internal diameter of tube (mm) = (patient's age in years + 16) / 4

• Appropriate depth of insertion of orotracheal tube (cm) = 12 + (patient's age in years / 2)

Tracheal intubation is generally considered the best method for airway management under a wide variety of circumstances, as it provides the most reliable means of oxygenation and ventilation and the greatest degree of protection against regurgitation and pulmonary aspiration.

Four anatomic features must be present for orotracheal intubation to be straightforward: adequate mouth opening (full range of motion of the temporomandibular joint), sufficient pharyngeal space (determined by examining the hypopharynx), sufficient submandibular space (distance between the thyroid cartilage and the chin, the space into which the tongue must be displaced in order for the larygoscopist to view the glottis), and adequate extension of the cervical spine at the atlanto-occipital joint. If any of these variables is in any way compromised, intubation should be expected to be difficult.

Minor complications are common after laryngoscopy and insertion of an orotracheal tube. These are typically of short duration, such as sore throat, lacerations of the lips or gums or other structures within the upper airway, chipped, fractured or dislodged teeth, nasal injury, Other complications which are common but potentially more serious include tachycardia, dysrhythmias, hypertension, elevated intracranial and introcular pressure, and bronchospasm.

Minor complications such as chipped, fractured or dislodged teeth, and lacerations of the gums or other structures within the upper airway are common after laryngoscopy and insertion of an orotracheal tube. More serious complications include laryngospasm, perforation of the trachea or esophagus, pulmonary aspiration of gastric contents or other foreign bodies, fracture or dislocation of the cervical spine, temporomandibular joint or arytenoid cartilages, decreased oxygen content, elevated arterial carbon dioxide, cardiac dysrhythmias, hypertension, increased intracranial or intraocular pressure and vocal cord paresis.

Complications may also be severe and long-lasting or permanent, such as vocal cord trauma, esophageal perforation and retropharyngeal abscess, bronchial intubation, or nerve injury. They may even be immediately life-threatening, such as laryngospasm and negative pressure pulmonary edema, aspiration, unrecognized esophageal intubation, or accidental disconnection or dislodgement of the tracheal tube).

Inability to secure the airway, with subsequent failure of oxygenation and ventilation is a life-threatening complication which if not immediately corrected leads to hypoxia, brain damage, cardiovascular collapse, and death.

One complication, unintentional and unrecognized intubation of the esophagus, is both common (as frequent as 25% in the hands of inexperienced personnel) and likely to result in a deleterious or even fatal outcome. In such cases, oxygen is inadvertently administered to the stomach, from where it cannot be taken up by the circulatory system, instead of the lungs. If this situation is not immediately identified and corrected, death will ensue from cerebral and cardiac anoxia.

Of 4,460 claims in the American Society of Anesthesiologists (ASA) Closed Claims Project database, 266 (approximately 6%) were for airway injury. Of these 266 cases, 87% of the injuries were temporary, 5% were permanent or disabling, and 8% resulted in death. Difficult intubation, age older than 60 years, and female gender were associated with claims for perforation of the esophagus or pharynx. Early signs of perforation were present in only 51% of perforation claims, whereas late sequelae occurred in 65%.

Although it the greatest degree of protection against regurgitation and pulmonary aspiration, tracheal intubation is not the only means to maintain a patent airway. Alternative techniques for airway management and delivery of oxygen or other breathing gases include the laryngeal mask airway, cuffed oropharyngeal airway, CPAP mask, nasal BiPAP mask, simple face mask, and the nasal cannula.

Tracheotomy

The earliest known depiction of a tracheotomy is found on two Egyptian tablets dating back to around 3600 BC.

The first detailed descriptions of tracheal intubation and subsequent artificial respiration of animals were from Andreas Vesalius (1514???1564) of Brussels. In his landmark book published in 1543, De humani corporis fabrica, he described an experiment in which he passed a reed into the trachea of a dying animal whose thorax had been opened and maintained ventilation by blowing into the reed intermittently.

Despite the many recorded instances of its use since antiquity , it was not until the early 19th century that the tracheotomy finally began to be recognized as a legitimate means of treating severe airway obstruction. In 1852, French physician Armand Trousseau (1801???1867) presented a series of 169 tracheotomies to the Acad??mie Imp??riale de M??decine . 158 of these were performed for the treatment of croup, and 11 were performed for "chronic maladies of the larynx"). Between 1830-1855, more than 350 tracheotomies were performed in Paris, most of them at the H??pital des Enfants Malades , a public hospital, with an overall survival rate of only 20-25%. 58% (14 of 24) patients in Trousseau's private practice survived the operation however, largely because of better postoperative care.

In 1871, the German surgeon Friedrich Trendelenburg (1844???1924) published a paper describing the first successful elective human tracheotomy to be performed for the purpose of administration of general anesthesia.

Laryngoscopy and non-surgical techniques

In 1854, a Spanish singing teacher named Manuel Garc??a (1805???1906) became the first man to view the functioning glottis in a living human.

In 1913, Chevalier Jackson was the first to report a high rate of success for the use of direct laryngoscopy as a means to intubate the trachea.

Between 1945 and 1952, optical engineers built upon the earlier work of Rudolph Schindler (1888???1968), developing the first gastrocamera. The digital revolution of the 21st century has brought newer technology to the art and science of tracheal intubation. Several manufacturers have developed video laryngoscopes which employ digital technology such as the CMOS active pixel sensor (CMOS APS) to generate a view of the glottis so that the trachea may be intubated.

General

Specific

• Videos of direct laryngoscopy recorded with the Airway Cam (TM) imaging system

• Examples of some devices for facilitation of tracheal intubation

• Diagram of performance of the Sellick maneuver